// SPDX-FileCopyrightText: 2024 Himbeer <himbeer@disroot.org>
//
// SPDX-License-Identifier: AGPL-3.0-or-later

const std = @import("std");

const instructions = @import("instructions.zig");
const paging = @import("paging.zig");
const process = @import("process.zig");
const sysexchange = @import("sysexchange.zig");
const trap = @import("trap.zig");
const vfs = @import("vfs.zig");

pub const Error = error{
    Unimplemented,
};

pub const HandleError = error{
    UnknownSyscall,
};

pub fn handler(proc: *process.Info, trap_frame: *trap.Frame) !void {
    const ret = sysexchange.frameReturn;
    switch (trap_frame.general_purpose_registers[17]) {
        100000 => ret(null, trap_frame, uprint(trap_frame)),
        100001 => ret(null, trap_frame, open(proc, trap_frame)),
        100002 => ret(null, trap_frame, close(proc, trap_frame)),
        100003 => ret(null, trap_frame, provideStream(proc, trap_frame)),
        100004 => ret(null, trap_frame, provideFile(proc, trap_frame)),
        100005 => ret(null, trap_frame, provideHook(proc, trap_frame)),
        100006 => ret(null, trap_frame, mkdir(proc, trap_frame)),
        100007 => ret(null, trap_frame, provideDirHook(proc, trap_frame)),
        100008 => ret(null, trap_frame, remove(trap_frame)),
        100009 => ret(null, trap_frame, read(proc, trap_frame)),
        100010 => ret(null, trap_frame, write(proc, trap_frame)),
        100011 => ret(null, trap_frame, list(proc, trap_frame)),
        100012 => ret(null, trap_frame, terminate(proc)),
        100013 => ret(null, trap_frame, processId(proc)),
        else => return HandleError.UnknownSyscall,
    }
}

// uprint(str_addr: usize, len: usize) void
fn uprint(trap_frame: *const trap.Frame) void {
    const procmem: *paging.Table = @ptrFromInt(instructions.satp.read().ppn << 12);

    const paddr = procmem.translate(trap_frame.general_purpose_registers[10]).?;

    const str_ptr: [*]const u8 = @ptrFromInt(paddr);
    const str = str_ptr[0..trap_frame.general_purpose_registers[11]];

    const w = @import("Console.zig").autoChoose().?.writer();
    w.print("User message: {s}\r\n", .{str}) catch unreachable;
}

// open(path_c: [*:0]const u8, data: usize) Result(usize) // fixme: Kernel panic if null pointer
fn open(proc: *process.Info, trap_frame: *trap.Frame) void {
    paging.setUserMemoryAccess(true);
    defer paging.setUserMemoryAccess(false);

    const path_c: [*:0]const u8 = @ptrFromInt(trap_frame.general_purpose_registers[10]);
    const data = trap_frame.general_purpose_registers[11];

    const result = vfs.openZ(proc, path_c, data) catch |err| {
        sysexchange.frameReturn(usize, trap_frame, err);
        return;
    };

    switch (result) {
        .rd => |rd| {
            const maybe_handle = proc.createRdHandle(rd);
            sysexchange.frameReturn(usize, trap_frame, maybe_handle);
        },
        .data => |result_data| {
            sysexchange.frameReturn(null, trap_frame, result_data);
        },
    }
}

// close(handle: usize) void
fn close(proc: *process.Info, trap_frame: *const trap.Frame) void {
    const handle = trap_frame.general_purpose_registers[10];
    proc.destroyRdHandle(handle);
}

// provideStream(
//     path_c: [*:0]const u8, // fixme: Kernel panic if null pointer
//     options: *const vfs.Options, // fixme: Kernel panic if null pointer
//     readFn: ?vfs.Stream.ReadFn,
//     writeFn: ?vfs.Stream.WriteFn,
// ) Result(void)
fn provideStream(proc: *const process.Info, trap_frame: *trap.Frame) void {
    paging.setUserMemoryAccess(true);
    defer paging.setUserMemoryAccess(false);

    const path_c: [*:0]const u8 = @ptrFromInt(trap_frame.general_purpose_registers[10]);
    const options: *const vfs.Options = @ptrFromInt(trap_frame.general_purpose_registers[11]);
    const readFn: ?vfs.Stream.ReadFn = @ptrFromInt(trap_frame.general_purpose_registers[12]);
    const writeFn: ?vfs.Stream.WriteFn = @ptrFromInt(trap_frame.general_purpose_registers[13]);

    sysexchange.frameReturn(null, trap_frame, vfs.provideResourceZ(path_c, .{
        .tag = .stream,
        .data = .{ .stream = .{
            .readFn = readFn,
            .writeFn = writeFn,
        } },
    }, proc.id, options.*));
}

// provideFile(
//     path_c: [*:0]const u8, // fixme: Kernel panic if null pointer
//     options: *const vfs.Options, // fixme: Kernel panic if null pointer
//     readFn: ?vfs.File.ReadFn,
//     writeFn: ?vfs.File.WriteFn,
//     closeFn: ?vfs.File.CloseFn,
//     initializer: ?*anyopaque,
// ) Result(void)
fn provideFile(proc: *const process.Info, trap_frame: *trap.Frame) void {
    paging.setUserMemoryAccess(true);
    defer paging.setUserMemoryAccess(false);

    const path_c: [*:0]const u8 = @ptrFromInt(trap_frame.general_purpose_registers[10]);
    const options: *const vfs.Options = @ptrFromInt(trap_frame.general_purpose_registers[11]);
    const readFn: ?vfs.File.ReadFn = @ptrFromInt(trap_frame.general_purpose_registers[12]);
    const writeFn: ?vfs.File.WriteFn = @ptrFromInt(trap_frame.general_purpose_registers[13]);
    const closeFn: ?vfs.File.CloseFn = @ptrFromInt(trap_frame.general_purpose_registers[14]);
    const initializer: ?*anyopaque = @ptrFromInt(trap_frame.general_purpose_registers[15]);

    sysexchange.frameReturn(null, trap_frame, vfs.provideResourceZ(path_c, .{
        .tag = .file,
        .data = .{ .file = .{
            .readFn = readFn,
            .writeFn = writeFn,
            .closeFn = closeFn,
            .initializer = initializer,
        } },
    }, proc.id, options.*));
}

// provideHook(
//     path_c: [*:0]const u8, // fixme: Kernel panic if null pointer
//     options: *const vfs.Options, // fixme: Kernel panic if null pointer,
//     callback: vfs.Hook.Callback,
// ) Result(void)
fn provideHook(proc: *const process.Info, trap_frame: *trap.Frame) void {
    paging.setUserMemoryAccess(true);
    defer paging.setUserMemoryAccess(false);

    const path_c: [*:0]const u8 = @ptrFromInt(trap_frame.general_purpose_registers[10]);
    const options: *const vfs.Options = @ptrFromInt(trap_frame.general_purpose_registers[11]);
    const callback: vfs.Hook.Callback = @ptrFromInt(trap_frame.general_purpose_registers[12]);

    sysexchange.frameReturn(null, trap_frame, vfs.provideResourceZ(path_c, .{
        .tag = .hook,
        .data = .{ .hook = .{
            .callback = callback,
        } },
    }, proc.id, options.*));
}

// mkdir(
//     path_c: [*:0]const u8, // fixme: Kernel panic if null pointer
// ) Result(void)
fn mkdir(proc: *const process.Info, trap_frame: *trap.Frame) void {
    const path_c: [*:0]const u8 = @ptrFromInt(trap_frame.general_purpose_registers[10]);

    const allocator = vfs.treeRoot().allocator;
    const tree = allocator.create(vfs.Tree) catch |err| {
        sysexchange.frameReturn(void, trap_frame, err);
        return;
    };
    tree.* = vfs.Tree.init(allocator);

    sysexchange.frameReturn(null, trap_frame, vfs.provideResourceZ(path_c, .{
        .tag = .dir,
        .data = .{ .dir = tree },
    }, proc.id, .{
        .reclaimable = false,
    }));
}

// provideDirHook(
//     path_c: [*:0]const u8, // fixme: Kernel panic if null pointer
//     options: *const vfs.Options, // fixme: Kernel panic if null pointer
//     provideFn: vfs.DirHook.ProvideFn,
//     findFn: vfs.DirHook.FindFn,
//     listFn:vfs.DirHook.ListFn,
//     removeFn: vfs.DirHook.RemoveFn,
// ) Result(void)
fn provideDirHook(proc: *const process.Info, trap_frame: *trap.Frame) void {
    paging.setUserMemoryAccess(true);
    defer paging.setUserMemoryAccess(false);

    const path_c: [*:0]const u8 = @ptrFromInt(trap_frame.general_purpose_registers[10]);
    const options: *const vfs.Options = @ptrFromInt(trap_frame.general_purpose_registers[11]);
    const provideFn: vfs.DirHook.ProvideFn = @ptrFromInt(trap_frame.general_purpose_registers[12]);
    const findFn: vfs.DirHook.FindFn = @ptrFromInt(trap_frame.general_purpose_registers[13]);
    const listFn: vfs.DirHook.ListFn = @ptrFromInt(trap_frame.general_purpose_registers[14]);
    const removeFn: vfs.DirHook.RemoveFn = @ptrFromInt(trap_frame.general_purpose_registers[15]);

    sysexchange.frameReturn(null, trap_frame, vfs.provideResourceZ(path_c, .{
        .tag = .dir_hook,
        .data = .{ .dir_hook = .{
            .provideFn = provideFn,
            .findFn = findFn,
            .listFn = listFn,
            .removeFn = removeFn,
        } },
    }, proc.id, options.*));
}

// remove(path_c: [*:0]const u8) Result(void) // fixme: Kernel panic if null pointer
fn remove(trap_frame: *trap.Frame) void {
    const path_c: [*:0]const u8 = @ptrFromInt(trap_frame.general_purpose_registers[10]);
    const path = std.mem.sliceTo(path_c, 0);
    const dirname = std.fs.path.dirnamePosix(path) orelse "/";

    if (vfs.find(dirname)) |inode| {
        const basename = std.fs.path.basenamePosix(path);
        removeFrom(trap_frame, inode, basename);
    } else {
        sysexchange.frameReturn(void, trap_frame, vfs.Error.NotFound);
    }
}

fn removeFrom(trap_frame: *trap.Frame, inode: *vfs.Inode, basename: []const u8) void {
    switch (inode.resource.tag) {
        .dir => {
            const dir = inode.resource.data.dir;
            sysexchange.frameReturn(null, trap_frame, dir.remove(basename));
        },
        .dir_hook => {
            const dir_hook = inode.resource.data.dir_hook;

            const removeFn = dir_hook.removeFn orelse {
                sysexchange.frameReturn(void, trap_frame, vfs.Error.RemoveNotSupported);
                return;
            };
            const result = removeFn(basename.ptr, basename.len);
            sysexchange.frameReturnResult(void, trap_frame, result);
        },
        else => sysexchange.frameReturn(void, trap_frame, vfs.Error.NotADirectory),
    }
}

// read(handle: usize, buffer: [*]u8, len: usize) Result(usize)
fn read(proc: *process.Info, trap_frame: *trap.Frame) void {
    paging.setUserMemoryAccess(true);
    defer paging.setUserMemoryAccess(false);

    const handle = trap_frame.general_purpose_registers[10];
    const buffer: [*]u8 = @ptrFromInt(trap_frame.general_purpose_registers[11]);
    const len = trap_frame.general_purpose_registers[12];

    const rd = proc.rds.get(handle) orelse {
        sysexchange.frameReturn(usize, trap_frame, process.Error.BadRdHandle);
        return;
    };

    const result = rd.read(proc, buffer[0..len]) catch |err| blk: {
        if (err == vfs.Error.Orphaned) {
            proc.destroyRdHandle(handle);
        }

        break :blk err;
    };
    sysexchange.frameReturn(usize, trap_frame, result);
}

// write(handle: usize, bytes: [*]const u8, len: usize) Result(usize)
fn write(proc: *process.Info, trap_frame: *trap.Frame) void {
    paging.setUserMemoryAccess(true);
    defer paging.setUserMemoryAccess(false);

    const handle = trap_frame.general_purpose_registers[10];
    const bytes: [*]const u8 = @ptrFromInt(trap_frame.general_purpose_registers[11]);
    const len = trap_frame.general_purpose_registers[12];

    const rd = proc.rds.get(handle) orelse {
        sysexchange.frameReturn(usize, trap_frame, process.Error.BadRdHandle);
        return;
    };

    const result = rd.write(proc, bytes[0..len]) catch |err| blk: {
        if (err == vfs.Error.Orphaned) {
            proc.destroyRdHandle(handle);
        }

        break :blk err;
    };
    sysexchange.frameReturn(usize, trap_frame, result);
}

// list(path_c: [*:0]const u8, entries: [*]vfs.DirEntry, len: usize) Result(usize)
fn list(proc: *process.Info, trap_frame: *trap.Frame) void {
    // fixme: Kernel panic if null pointer
    const path_c: [*:0]const u8 = @ptrFromInt(trap_frame.general_purpose_registers[10]);
    // fixme: Kernel panic if null pointer
    const entries: [*]vfs.DirEntry = @ptrFromInt(trap_frame.general_purpose_registers[11]);
    const len = trap_frame.general_purpose_registers[12];

    const result = vfs.listZ(proc, path_c, entries[0..len]);
    sysexchange.frameReturn(null, trap_frame, result);
}

// terminate() void
fn terminate(proc: *process.Info) void {
    proc.terminate();
    process.schedule() catch |err| {
        std.debug.panic("Unable to schedule because all processes are terminated: {}", .{err});
    };
}

// processId() usize
fn processId(proc: *process.Info) usize {
    return proc.id;
}