const meta = @import("./meta.zig");
const stack = @import("./stack.zig");
const std = @import("std");

///
///
///
pub const Allocator = std.mem.Allocator;

///
/// File-system agnostic abstraction for manipulating a file.
///
pub const FileAccess = struct {
    context: *anyopaque,
    implementation: *const Implementation,

    ///
    /// Provides a set of implementation-specific behaviors to a [FileAccess] instance.
    ///
    pub const Implementation = struct {
        close: fn (*anyopaque) void,
        queryCursor: fn (*anyopaque) Error!u64,
        queryLength: fn (*anyopaque) Error!u64,
        read: fn (*anyopaque, []u8) Error!usize,
        seek: fn (*anyopaque, u64) Error!void,
        seekToEnd: fn (*anyopaque) Error!void,
        skip: fn (*anyopaque, i64) Error!void,
    };

    ///
    /// [Error.FileInaccessible] is a generic catch-all for a [FileAccess] reference no longer
    /// pointing to a file or the file becomming invalid for whatever reason.
    ///
    pub const Error = error {
        FileInaccessible,
    };

    ///
    /// Close the file referenced by `file_access` on the main thread, invalidating the reference to
    /// it and releasing any associated resources.
    ///
    /// Freeing an invalid `file_access` has no effect on the file and logs a warning over the
    /// wasted effort.
    ///
    pub fn close(file_access: FileAccess) void {
        return file_access.implementation.close(file_access.context);
    }

    ///
    /// Attempts to query the current cursor position for the file referenced by `file_access`.
    ///
    /// Returns the number of bytes into the file that the cursor is relative to its beginning or a
    /// [Error] on failure.
    ///
    pub fn queryCursor(file_access: FileAccess) Error!u64 {
        return file_access.implementation.queryCursor(file_access.context);
    }

    ///
    /// Attempts to query the current length for the file referenced by `file_access`.
    ///
    /// Returns the current length of the file at the time of the operation or a [Error] if the file
    /// failed to be queried.
    ///
    pub fn queryLength(file_access: FileAccess) Error!u64 {
        return file_access.implementation.queryLength(file_access.context);
    }

    ///
    /// Attempts to read `file_access` from the its current position into `buffer`.
    ///
    /// Returns the number of bytes that were available to be read, otherwise an [Error] on failure.
    ///
    pub fn read(file_access: FileAccess, buffer: []u8) Error!usize {
        return file_access.implementation.read(file_access.context, buffer);
    }

    ///
    /// Attempts to seek `file_access` from the beginning of the file to `cursor` bytes.
    ///
    /// Returns [Error] on failure.
    ///
    pub fn seek(file_access: FileAccess, cursor: u64) Error!void {
        return file_access.implementation.seek(file_access.context, cursor);
    }

    ///
    /// Attempts to seek `file_access` to the end of the file.
    ///
    /// Returns [Error] on failure.
    ///
    pub fn seekToEnd(file_access: FileAccess) Error!void {
        return file_access.implementation.seekToEnd(file_access.context);
    }

    ///
    /// Attempts to seek `file_access` by `offset` from the current file position.
    ///
    /// Returns [Error] on failure;
    ///
    pub fn skip(file_access: FileAccess, offset: i64) Error!void {
        return file_access.implementation.skip(file_access.context, offset);
    }
};

///
/// Closure that captures a reference to readable resources like block devices, memory buffers,
/// network sockets, and more.
///
pub const Reader = meta.Function(@sizeOf(usize), []u8, usize);

///
/// Returns a state machine for lazily computing all `Element` components of a given source input
/// that match a delimiting pattern.
///
pub fn Spliterator(comptime Element: type) type {
    return struct {
        source: []const Element,
        delimiter: []const Element,

        const Self = @This();

        ///
        /// Returns `true` if there is more data to be processed, otherwise `false`.
        ///
        pub fn hasNext(self: Self) bool {
            return (self.source.len != 0);
        }

        ///
        /// Iterates on `self` and returns the next view of [Spliterator.source] that matches
        /// [Spliterator.delimiter], or `null` if there is no more data to be processed.
        ///
        pub fn next(self: *Self) ?[]const Element {
            if (!self.hasNext()) return null;

            if (std.mem.indexOfPos(Element, self.source, 0, self.delimiter)) |index| {
                defer self.source = self.source[(index + self.delimiter.len) .. self.source.len];

                return self.source[0 .. index];
            }

            defer self.source = self.source[self.source.len .. self.source.len];

            return self.source;
        }
    };
}

test "Spliterating text" {
    const testing = std.testing;

    // Single-character delimiter.
    {
        var spliterator = Spliterator(u8){
            .source = "single.character.separated.hello.world",
            .delimiter = ".",
        };

        const components = [_][]const u8{"single", "character", "separated", "hello", "world"};
        var index = @as(usize, 0);

        while (spliterator.next()) |split| : (index += 1) {
            try testing.expect(std.mem.eql(u8, split, components[index]));
        }
    }

    // Multi-character delimiter.
    {
        var spliterator = Spliterator(u8){
            .source = "finding a needle in a needle stack",
            .delimiter = "needle",
        };

        const components = [_][]const u8{"finding a ", " in a ", " stack"};
        var index = @as(usize, 0);

        while (spliterator.next()) |split| : (index += 1) {
            try testing.expect(std.mem.eql(u8, split, components[index]));
        }
    }
}

///
/// Closure that captures a reference to writable resources like block devices, memory buffers,
/// network sockets, and more.
///
pub const Writer = meta.Function(@sizeOf(usize), []const u8, usize);

///
/// Returns `true` if `this` is the same length and contains the same data as `that`, otherwise
/// `false`.
///
pub fn equals(comptime Element: type, this: []const Element, that: []const Element) bool {
    if (this.len != that.len) return false;

    {
        var i = std.mem.zeroes(usize);

        while (i < this.len) : (i += 1) if (this[i] != that[i]) return false;
    }

    return true;
}

test "Memory buffers equal" {
    const bytes_sequence = &.{69, 42, 0};
    const testing = std.testing;

    try testing.expect(equals(u8, bytes_sequence, bytes_sequence));
    try testing.expect(!equals(u8, bytes_sequence, &.{69, 42}));
}

///
/// Returns a deterministic hash code compiled from each byte in `bytes`.
///
/// **Note** that this operation has `O(n)` time complexity.
///
pub fn hashBytes(bytes: []const u8) usize {
    var hash = @as(usize, 5381);

    for (bytes) |byte| hash = ((hash << 5) + hash) + byte;

    return hash;
}

test "Hashing bytes" {
    const bytes_sequence = &.{69, 42, 0};
    const testing = std.testing;

    try testing.expect(hashBytes(bytes_sequence) == hashBytes(bytes_sequence));
    try testing.expect(hashBytes(bytes_sequence) != hashBytes(&.{69, 42}));
}

///
/// Returns a [Writer] that silently consumes all given data without failure and throws it away.
///
/// This is commonly used for testing or redirected otherwise unwanted output data that has to be
/// sent somewhere for whatever reason.
///
pub fn nullWriter() Writer {
    return Writer.capture(std.mem.zeroes(usize), struct {
        fn write(_: usize, buffer: []const u8) usize {
            return buffer.len;
        }
    }.write);
}

test "Null writing" {
    const testing = std.testing;

    {
        const sequence = "foo";

        try testing.expectEqual(nullWriter().apply(sequence), sequence.len);
    }
}