diff --git a/.gitignore b/.gitignore
index 3542e5b..d3c2c1b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+<<<<<<< HEAD
 # ---> Swift
 # Xcode
 #
@@ -5,60 +6,8 @@
 
 ## User settings
 xcuserdata/
-
-## Obj-C/Swift specific
-*.hmap
-
-## App packaging
-*.ipa
-*.dSYM.zip
-*.dSYM
-
-## Playgrounds
-timeline.xctimeline
-playground.xcworkspace
-
-# Swift Package Manager
-#
-# Add this line if you want to avoid checking in source code from Swift Package Manager dependencies.
-# Packages/
-# Package.pins
-# Package.resolved
-# *.xcodeproj
-#
-# Xcode automatically generates this directory with a .xcworkspacedata file and xcuserdata
-# hence it is not needed unless you have added a package configuration file to your project
-# .swiftpm
-
-.build/
-
-# CocoaPods
-#
-# We recommend against adding the Pods directory to your .gitignore. However
-# you should judge for yourself, the pros and cons are mentioned at:
-# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
-#
-# Pods/
-#
-# Add this line if you want to avoid checking in source code from the Xcode workspace
-# *.xcworkspace
-
-# Carthage
-#
-# Add this line if you want to avoid checking in source code from Carthage dependencies.
-# Carthage/Checkouts
-
-Carthage/Build/
-
-# fastlane
-#
-# It is recommended to not store the screenshots in the git repo.
-# Instead, use fastlane to re-generate the screenshots whenever they are needed.
-# For more information about the recommended setup visit:
-# https://docs.fastlane.tools/best-practices/source-control/#source-control
-
-fastlane/report.xml
-fastlane/Preview.html
-fastlane/screenshots/**/*.png
-fastlane/test_output
-
+DerivedData/
+.swiftpm
+.netrc
+.vscode/
+**/*.swp
diff --git a/Package.swift b/Package.swift
new file mode 100644
index 0000000..dc2a5fe
--- /dev/null
+++ b/Package.swift
@@ -0,0 +1,33 @@
+// swift-tools-version: 6.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "Fishee",
+    dependencies:  [
+        .package(url: "https://github.com/apple/swift-argument-parser.git", .upToNextMajor(from: "1.5.0")),
+        .package(url: "https://github.com/duckdb/duckdb-swift", .upToNextMinor(from: .init(1, 1, 0))),
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package, defining a module or a test suite.
+        // Targets can depend on other targets in this package and products from dependencies.
+        .executableTarget(
+            name: "Fishee",
+            dependencies: [
+                .product(name: "ArgumentParser", package: "swift-argument-parser"),
+                .product(name: "DuckDB", package: "duckdb-swift"),
+            ],
+            path: "Sources"
+        ),
+        .testTarget(
+            name: "FisheeTests",
+            dependencies: ["Fishee"],
+            path: "Tests",
+            resources: [
+                .copy("Resources/fish_history_test.txt"),
+                .copy("Resources/fish_history_test_2.txt"),
+            ]
+        )
+    ]
+)
diff --git a/Sources/Algebra.swift b/Sources/Algebra.swift
new file mode 100644
index 0000000..75b883a
--- /dev/null
+++ b/Sources/Algebra.swift
@@ -0,0 +1,41 @@
+//
+// Copyright © 2024 Salar Rahmanian.
+//	    
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+//      http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+import Foundation
+	
+struct FishHistoryEntry: Equatable {
+    let cmd: String
+    let when: Int
+    let paths: [String]
+    
+    func getDate() -> Date {
+        Date(timeIntervalSince1970: TimeInterval(when))
+    }
+    
+    func writeEntry() -> [String] {
+        var output: [String] = []
+        
+        output.append("- cmd: \(cmd)")
+        output.append("  when: \(when)")
+        
+        if !paths.isEmpty {
+            output.append("  paths:")
+            paths.forEach { output.append("    - \(String($0))") }
+        }
+        
+        return output
+    }
+}
diff --git a/Sources/FileHelpers.swift b/Sources/FileHelpers.swift
new file mode 100644
index 0000000..42e0a94
--- /dev/null
+++ b/Sources/FileHelpers.swift
@@ -0,0 +1,38 @@
+//
+// Copyright © 2024 Salar Rahmanian.
+//	    
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+//      http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+// limitations under the License.
+//
+	
+
+import Foundation
+
+
+func getPath(_ pathStr: String) -> URL? {
+    let userHomeDirectory = FileManager.default.homeDirectoryForCurrentUser.path
+    var filePath: String = pathStr
+    
+    if pathStr.hasPrefix("~") {
+        filePath = (pathStr as NSString).expandingTildeInPath
+    }
+    
+    if pathStr.hasPrefix("$HOME") {
+        filePath = filePath.replacingOccurrences(of: "$HOME", with: userHomeDirectory)
+    }
+    
+    if !FileManager.default.fileExists(atPath: filePath) {
+        return nil
+    }
+    
+    return URL(fileURLWithPath: filePath)
+}
diff --git a/Sources/Fishee.swift b/Sources/Fishee.swift
new file mode 100644
index 0000000..4e5d7eb
--- /dev/null
+++ b/Sources/Fishee.swift
@@ -0,0 +1,103 @@
+//
+// Copyright © 2024 Salar Rahmanian.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+
+import ArgumentParser
+import Foundation
+
+let DEFAULT_FISH_HISTORY_LOCATION: String = "~/.local/share/fish/fish_history"
+
+@main
+struct Fishee: ParsableCommand {
+    @Option(name: [.short, .customLong("history-file")], help: "Location of your fish history file. Will default to ~/.local/share/fish/fish_history")
+    var fishHistoryLocationStr: String?
+    
+    @Option(name: .shortAndLong, help: "File path to file to merge with history file.")
+    var mergeFile: String?
+    
+    @Option(
+        name: [.short, .customLong("output-file")],
+        help: "File to write to. Default: same as current history file."
+    )
+    var writeFileStr: String?
+    
+    @Flag(
+        name: .shortAndLong,
+        help: "Dry run. Will only print to the console without actually modifying the history file."
+    )
+    var dryRun: Bool = false
+    
+    @Flag(
+        name: .shortAndLong,
+        help: "Remove duplicates from combined history. Default: false"
+    )
+    var removeDuplicates: Bool = false
+    
+    @Flag(
+        name: .shortAndLong,
+        inversion: .prefixedNo,
+        help: "Backup fish history file given before writing."
+    )
+    var backup: Bool = true
+    
+    var fishHistoryLocation: URL? {
+        let pathStr = fishHistoryLocationStr ?? DEFAULT_FISH_HISTORY_LOCATION
+        return getPath(pathStr)
+    }
+    
+    var writeFileLocation: URL? {
+        let pathStr = writeFileStr ?? DEFAULT_FISH_HISTORY_LOCATION
+        return getPath(pathStr)
+    }
+    
+    public func run() throws {
+        let mergeFileLocation = mergeFile.flatMap { getPath($0) }
+        let finalHistory: [FishHistoryEntry] = switch (fishHistoryLocation, mergeFileLocation) {
+        case let (fishHistoryLocation?, mergeFileLocation?):
+            {
+                let currentHistory = parseFishHistory(from: fishHistoryLocation.path) ?? []
+                let toMergeHistory = parseFishHistory(from: mergeFileLocation.path) ?? []
+                return mergeFishHistory(currentHistory, toMergeHistory, removeDuplicates: removeDuplicates)
+            }()
+        case let (fishHistoryLocation?, nil):
+            parseFishHistory(from: fishHistoryLocation.path) ?? []
+        default:
+            []
+        }
+        
+        if dryRun {
+            finalHistory.forEach { print("\($0.writeEntry().joined(separator: "\n"))") }
+        }
+        else {
+            if let writePath = writeFileLocation?.path {
+                let result = writeFishHistory(
+                    to: writePath,
+                    history: finalHistory,
+                    historyFileLocation: fishHistoryLocation?.path,
+                    backup: backup
+                )
+                if result {
+                    print("Succussfully updated \(writePath)")
+                }
+                else {
+                    print("Failed to update \(writePath)")
+                }
+            }
+        }
+        
+        return
+    }
+}
diff --git a/Sources/Parser.swift b/Sources/Parser.swift
new file mode 100644
index 0000000..60efe51
--- /dev/null
+++ b/Sources/Parser.swift
@@ -0,0 +1,131 @@
+//
+// Copyright © 2024 Salar Rahmanian.
+//	    
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+//      http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+// limitations under the License.
+//
+	
+
+import Foundation
+
+
+func backupHistory(_ path: String) -> Bool {
+    let fileManager = FileManager.default
+        
+    guard fileManager.fileExists(atPath: path) else {
+        print("File does not exist at path: \(path)")
+        return false
+    }
+    
+    let fileURL = URL(fileURLWithPath: path)
+    let fileExtension = fileURL.pathExtension
+    let fileNameWithoutExtension = fileURL.deletingPathExtension().lastPathComponent
+    let directory = fileURL.deletingLastPathComponent()
+    
+    let newFileName = "\(fileNameWithoutExtension)_copy"
+    let newFileURL = directory.appendingPathComponent(newFileName).appendingPathExtension(fileExtension)
+    
+    do {
+        try fileManager.copyItem(at: fileURL, to: newFileURL)
+        print("File duplicated successfully to: \(newFileURL.path)")
+        return true
+    } catch {
+        return false
+    }
+}
+
+
+func writeFishHistory(to path: String, history: [FishHistoryEntry], historyFileLocation: String?, backup: Bool = true) -> Bool {
+    var output = ""
+    
+    if backup {
+        if let backupFile = historyFileLocation {
+            let result = backupHistory(backupFile)
+            if !result {
+                print("Failed to backup \(backupFile) so aborting!")
+                return false
+            }
+        }
+    }
+    
+    history.forEach { output += $0.writeEntry().joined(separator: "\n") + "\n" }
+    
+    if !output.isEmpty {
+        do {
+            try output.write(toFile: path, atomically: true, encoding: .utf8)
+            print("Successfully wrote merged history to \(path)")
+            return true
+        } catch {
+            print("Error writing merged history: \(error)")
+            return false
+        }
+    }
+    else {
+        print("Nothing to write to \(path)")
+        return false
+    }
+}
+
+func parseFishHistory(from filePath: String) -> [FishHistoryEntry]? {
+    guard let fileContents = try? String(contentsOfFile: filePath) else {
+        print("Failed to open file.")
+        return nil
+    }
+    
+    let lines = fileContents.split(separator: "\n").map { String($0).trimmingCharacters(in: .whitespaces) }
+
+    let initialState: (entries: [FishHistoryEntry], currentCmd: String?, currentWhen: Int?, currentPaths: [String]) = ([], nil, nil, [])
+    
+    let result = lines.reduce(into: initialState) { state, line in
+        if line.starts(with: "- cmd:") {
+            if let cmd = state.currentCmd, let when = state.currentWhen {
+                let entry = FishHistoryEntry(cmd: cmd, when: when, paths: state.currentPaths)
+                state.entries.append(entry)
+                state.currentPaths = []
+            }
+            state.currentCmd = String(line.dropFirst("- cmd:".count).trimmingCharacters(in: .whitespaces))
+        } else if line.starts(with: "when:") {
+            if let whenValue = Int(line.dropFirst("when:".count).trimmingCharacters(in: .whitespaces)) {
+                state.currentWhen = whenValue
+            }
+        } else if line.starts(with: "paths:") {
+            return
+        } else if line.starts(with: "- ") {
+            let path = String(line.dropFirst("- ".count).trimmingCharacters(in: .whitespaces))
+            state.currentPaths.append(path)
+        }
+    }
+    
+    if let cmd = result.currentCmd, let when = result.currentWhen {
+        let entry = FishHistoryEntry(cmd: cmd, when: when, paths: result.currentPaths)
+        return result.entries + [entry]
+    }
+    
+    return result.entries
+}
+
+func mergeFishHistory(_ left: [FishHistoryEntry], _ right: [FishHistoryEntry], removeDuplicates: Bool = false) -> [FishHistoryEntry] {
+    
+    let merged = left + right
+    
+    if removeDuplicates {
+        let finalList = merged.reduce(into: [String:FishHistoryEntry]()) { result, entry in
+            if result[entry.cmd] == nil {
+                result[entry.cmd] = entry
+            }
+        }
+        return Array(finalList.values)
+    } else {
+        return merged
+    }
+    
+}
diff --git a/Tests/AlgebraTest.swift b/Tests/AlgebraTest.swift
new file mode 100644
index 0000000..1b9a0ac
--- /dev/null
+++ b/Tests/AlgebraTest.swift
@@ -0,0 +1,42 @@
+//
+// Copyright © 2024 Salar Rahmanian.
+//	    
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+//      http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+// limitations under the License.
+//
+	
+import Foundation
+import Testing
+@testable import Fishee
+
+@Suite
+final class AlgebraTests {
+    let historyItem = FishHistoryEntry(cmd: "cd Projects/Fishee/", when: 1727545693, paths: ["Projects/Fishee/"])
+
+    @Test func dateFromHistoryTest() {
+        let gotDate = historyItem.getDate()
+        #expect(gotDate == Date(timeIntervalSince1970: 1727545693))
+    }
+    
+    @Test func writeEntryTest() {
+        let entry = historyItem.writeEntry()
+        #expect(entry.count > 0)
+        let expectedEntry = """
+        - cmd: cd Projects/Fishee/
+          when: 1727545693
+          paths:
+            - Projects/Fishee/
+        """
+        #expect(entry.joined(separator: "\n") == expectedEntry)
+    }
+    
+}
diff --git a/Tests/FileHelpersTests.swift b/Tests/FileHelpersTests.swift
new file mode 100644
index 0000000..223a5e7
--- /dev/null
+++ b/Tests/FileHelpersTests.swift
@@ -0,0 +1,47 @@
+//
+// Copyright © 2024 Salar Rahmanian.
+//	    
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+//      http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+// limitations under the License.
+//
+	
+import Foundation
+import Testing
+@testable import Fishee
+
+
+final class FileHelpersTests {
+    let filePath = FileManager.default.homeDirectoryForCurrentUser.appendingPathComponent("myfile.txt")
+    
+    init() {
+        try? "this is a test".write(
+            to: filePath,
+            atomically: true,
+            encoding: .utf8
+        )
+    }
+    
+    deinit {
+        try? FileManager.default.removeItem(at: filePath)
+    }
+    
+    @Test(arguments: [
+        "$HOME/myfile.txt",
+        "~/myfile.txt",
+        "\(FileManager.default.homeDirectoryForCurrentUser.path)/myfile.txt"
+    ])
+    func getPathTest(testPath: String) {
+        let path = getPath(testPath)
+        let expected =  URL(fileURLWithPath: "\(FileManager.default.homeDirectoryForCurrentUser.path)/myfile.txt")
+        #expect(path == expected)
+    }
+}
diff --git a/Tests/ParserTests.swift b/Tests/ParserTests.swift
new file mode 100644
index 0000000..87f3891
--- /dev/null
+++ b/Tests/ParserTests.swift
@@ -0,0 +1,90 @@
+//
+// Copyright © 2024 Salar Rahmanian.
+//	    
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+//      http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+// limitations under the License.
+//
+	
+import Foundation
+import Testing
+@testable import Fishee
+
+@Suite
+final class ParserTests {
+    let fishHistoryFile = Bundle.module.path(forResource: "fish_history_test", ofType: "txt")
+    let historyItem = FishHistoryEntry(cmd: "cd Projects/Fishee/", when: 1727545693, paths: ["Projects/Fishee/"])
+    let historyItem2 = FishHistoryEntry(cmd: "swift package tools-version", when: 1727545709, paths: [])
+    let filePathforWriteTest = FileManager.default.urls(for: .downloadsDirectory, in: .userDomainMask)[0].appendingPathComponent(
+        "myfile.txt"
+    )
+    let filePathforFileBackupTest = FileManager.default.urls(for: .downloadsDirectory, in: .userDomainMask)[0].appendingPathComponent(
+        "myfile.txt_copy"
+    )
+    
+    deinit {
+        if FileManager.default.fileExists(atPath: filePathforWriteTest.path) {
+            _ = try? FileManager.default.removeItem(at: filePathforWriteTest)
+        }
+        if FileManager.default.fileExists(atPath: filePathforFileBackupTest.path) {
+            _ = try? FileManager.default.removeItem(at: filePathforFileBackupTest)
+        }
+    }
+
+    @Test func parseFishHistoryTest() {
+        #expect(fishHistoryFile != nil)
+        let fishHistory = parseFishHistory(from: fishHistoryFile!)
+        #expect(fishHistory!.count > 0)
+        let expectedHistory = [historyItem, historyItem2]
+        #expect(fishHistory == expectedHistory)
+    }
+    
+    @Test func writeFishHistoryTest() {
+        let written = writeFishHistory(
+            to: filePathforWriteTest.path,
+            history: [historyItem],
+            historyFileLocation: fishHistoryFile
+        )
+        #expect(written)
+        
+        let fileContent = try? String(contentsOf: filePathforWriteTest, encoding: .utf8)
+        let expectedEntry = """
+        - cmd: cd Projects/Fishee/
+          when: 1727545693
+          paths:
+            - Projects/Fishee/
+        
+        """
+        #expect(fileContent == expectedEntry)
+        #expect(FileManager.default.fileExists(atPath: filePathforFileBackupTest.path))
+    }
+    
+    @Test func mergeFishHistoryTest() {
+        let merged = mergeFishHistory([historyItem], [historyItem2])
+        #expect(merged.count == 2)
+        #expect(merged.contains(historyItem))
+        #expect(merged.contains(historyItem2))
+    }
+    
+    @Test func mergeFishHistoryWithDuplicateTest() {
+        let merged = mergeFishHistory([historyItem], [historyItem, historyItem2])
+        #expect(merged.count == 3)
+        #expect(merged.contains(historyItem))
+        #expect(merged.contains(historyItem2))
+    }
+
+    @Test func mergeFishHistoryRemoveDuplicateTest() {
+        let merged = mergeFishHistory([historyItem], [historyItem, historyItem2], removeDuplicates: true)
+        #expect(merged.count == 2)
+        #expect(merged.contains(historyItem))
+        #expect(merged.contains(historyItem2))
+    }
+}
diff --git a/Tests/Resources/fish_history_test.txt b/Tests/Resources/fish_history_test.txt
new file mode 100644
index 0000000..a007c1e
--- /dev/null
+++ b/Tests/Resources/fish_history_test.txt
@@ -0,0 +1,7 @@
+- cmd: cd Projects/Fishee/
+  when: 1727545693
+  paths:
+    - Projects/Fishee/
+- cmd: swift package tools-version
+  when: 1727545709
+
diff --git a/Tests/Resources/fish_history_test_2.txt b/Tests/Resources/fish_history_test_2.txt
new file mode 100644
index 0000000..0dddc9f
--- /dev/null
+++ b/Tests/Resources/fish_history_test_2.txt
@@ -0,0 +1,6 @@
+- cmd: gh pr create
+  when: 1727024167
+- cmd: nix flake update
+  when: 1727140536
+- cmd: swift package tools-version
+  when: 1727545709