use crate::component::{Component, RunError};
use crate::input::RawMode;

/// A sequential composition of interactive components.
///
/// Each step runs one `Component` to completion, then passes its result
/// to a continuation that produces the next `Flow`. The whole thing resolves
/// to a single `R` when complete.
///
/// # Example
///
/// ```rust,ignore
/// use sly::flow::Flow;
/// use sly::widgets::text_input::{text_input, TextInput};
/// use sly::widgets::confirm::confirm_str;
///
/// let flow: Flow<Option<String>> = Flow::step(
///     text_input(TextInput::new().prompt("Name: ")),
///     |name| {
///         Flow::step(
///             confirm_str(&format!("Save as '{}'?", name), true),
///             move |ok| {
///                 if ok { Flow::done(Some(name)) } else { Flow::done(None) }
///             },
///         )
///     },
/// );
///
/// let result = flow.run(&raw_mode).unwrap();
/// ```
pub struct Flow<R: 'static> {
    inner: Box<dyn FnOnce(&RawMode) -> Result<R, RunError>>,
}

impl<R: 'static> Flow<R> {
    /// Run one component step, then pass its result to a continuation.
    pub fn step<S, T>(component: Component<S, T>, then: impl FnOnce(T) -> Flow<R> + 'static) -> Self
    where
        S: 'static,
        T: 'static,
    {
        Flow {
            inner: Box::new(move |mode| {
                let result = component.run(mode)?;
                (then(result)).run(mode)
            }),
        }
    }

    /// A flow that immediately succeeds with `value`.
    pub fn done(value: R) -> Self {
        Flow {
            inner: Box::new(move |_mode| Ok(value)),
        }
    }

    /// A flow that immediately fails with `Cancelled`.
    pub fn cancel() -> Self {
        Flow {
            inner: Box::new(|_mode| Err(RunError::Cancelled)),
        }
    }

    /// Map the result value.
    pub fn map<R2: 'static>(self, f: impl FnOnce(R) -> R2 + 'static) -> Flow<R2> {
        Flow {
            inner: Box::new(move |mode| self.run(mode).map(f)),
        }
    }

    /// Run the entire flow to completion.
    pub fn run(self, mode: &RawMode) -> Result<R, RunError> {
        (self.inner)(mode)
    }
}

// ---------------------------------------------------------------------------
// Helper shorthands
// ---------------------------------------------------------------------------

use crate::widgets::confirm::confirm_str;
use crate::widgets::selector::{Selector, SelectorItem, selector};
use crate::widgets::text_input::{TextInput, text_input};

/// Run a text-input prompt as a single flow step.
pub fn ask(prompt: &str, input: TextInput) -> Flow<String> {
    let prompt = prompt.to_owned();
    let ti = input.prompt(&prompt);
    Flow::step(text_input(ti), Flow::done)
}

/// Run a selector as a single flow step.
pub fn choose<T: Clone + 'static>(items: Vec<SelectorItem<T>>) -> Flow<T> {
    let sel = Selector::new(items);
    Flow::step(selector(sel), Flow::done)
}

/// Run a yes/no confirmation as a single flow step.
pub fn confirm(message: &str, default: bool) -> Flow<bool> {
    Flow::step(confirm_str(message, default), Flow::done)
}

#[cfg(test)]
mod tests {
    use super::*;

    // We test Flow by constructing flows that don't touch a real terminal.
    // We use `Flow::done` and `Flow::cancel` directly, and test that `map`
    // and chaining work correctly via the inner closure without running
    // actual IO components.

    /// A helper that builds a Flow from a pre-computed result.
    #[allow(dead_code)]
    fn immediate<R: 'static>(r: Result<R, RunError>) -> Flow<R> {
        // We can't easily inject a raw mode, but we can test the logic of
        // done/cancel/map by relying on the fact that `done` and `cancel`
        // ignore the mode argument.
        match r {
            Ok(v) => Flow::done(v),
            Err(_) => Flow::cancel(),
        }
    }

    #[test]
    fn flow_done_produces_value() {
        // We can't call .run() without a RawMode, but we can verify the
        // structure: Flow::done wraps a closure that returns Ok(value).
        // Test indirectly via map.
        let f = Flow::done(42usize).map(|n| n * 2);
        // f is a Flow<usize>. We verify it's constructible.
        let _ = f; // just ensure it compiles without panicking
    }

    #[test]
    fn flow_map_transforms_result() {
        // Construct two immediate flows and chain them.
        let _f: Flow<String> = Flow::done(10usize).map(|n| format!("val={}", n));
    }

    #[test]
    fn flow_step_chains() {
        // Build a flow that chains two done steps.
        let _f: Flow<String> = Flow::step(
            {
                use crate::component::Component;
                // A component whose run() we can't call in a unit test (needs RawMode),
                // so we just verify the type chain compiles.
                Component::new(
                    (),
                    |_| Block::text(vec![]),
                    |_, _key| crate::component::Update::Finish("hello".to_string()),
                )
            },
            |s: String| Flow::done(format!("got: {}", s)),
        );
    }

    #[test]
    fn flow_cancel_type_checks() {
        let _f: Flow<u32> = Flow::cancel();
    }

    use crate::block::Block;
}