use crate::decision::Decision;
use crate::error::Error;
use crate::error::Result;
use serde::Deserialize;
use serde::Serialize;
use shlex::try_join;
use std::any::Any;
use std::fmt::Debug;
use std::sync::Arc;

/// Matches a single command token, either a fixed string or one of several allowed alternatives.
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum PatternToken {
    Single(String),
    Alts(Vec<String>),
}

impl PatternToken {
    fn matches(&self, token: &str) -> bool {
        match self {
            Self::Single(expected) => expected == token,
            Self::Alts(alternatives) => alternatives.iter().any(|alt| alt == token),
        }
    }

    pub fn alternatives(&self) -> &[String] {
        match self {
            Self::Single(expected) => std::slice::from_ref(expected),
            Self::Alts(alternatives) => alternatives,
        }
    }
}

/// Prefix matcher for commands with support for alternative match tokens.
/// First token is fixed since we key by the first token in policy.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct PrefixPattern {
    pub first: Arc<str>,
    pub rest: Arc<[PatternToken]>,
}

impl PrefixPattern {
    pub fn matches_prefix(&self, cmd: &[String]) -> Option<Vec<String>> {
        let pattern_length = self.rest.len() + 1;
        if cmd.len() < pattern_length || cmd[0] != self.first.as_ref() {
            return None;
        }

        for (pattern_token, cmd_token) in self.rest.iter().zip(&cmd[1..pattern_length]) {
            if !pattern_token.matches(cmd_token) {
                return None;
            }
        }

        Some(cmd[..pattern_length].to_vec())
    }
}

#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub enum RuleMatch {
    PrefixRuleMatch {
        #[serde(rename = "matchedPrefix")]
        matched_prefix: Vec<String>,
        decision: Decision,
        /// Optional rationale for why this rule exists.
        ///
        /// This can be supplied for any decision and may be surfaced in different contexts
        /// (e.g., prompt reasons or rejection messages).
        #[serde(skip_serializing_if = "Option::is_none")]
        justification: Option<String>,
    },
    HeuristicsRuleMatch {
        command: Vec<String>,
        decision: Decision,
    },
}

impl RuleMatch {
    pub fn decision(&self) -> Decision {
        match self {
            Self::PrefixRuleMatch { decision, .. } => *decision,
            Self::HeuristicsRuleMatch { decision, .. } => *decision,
        }
    }
}

#[derive(Clone, Debug, Eq, PartialEq)]
pub struct PrefixRule {
    pub pattern: PrefixPattern,
    pub decision: Decision,
    pub justification: Option<String>,
}

pub trait Rule: Any + Debug + Send + Sync {
    fn program(&self) -> &str;

    fn matches(&self, cmd: &[String]) -> Option<RuleMatch>;

    fn as_any(&self) -> &dyn Any;
}

pub type RuleRef = Arc<dyn Rule>;

impl Rule for PrefixRule {
    fn program(&self) -> &str {
        self.pattern.first.as_ref()
    }

    fn matches(&self, cmd: &[String]) -> Option<RuleMatch> {
        self.pattern
            .matches_prefix(cmd)
            .map(|matched_prefix| RuleMatch::PrefixRuleMatch {
                matched_prefix,
                decision: self.decision,
                justification: self.justification.clone(),
            })
    }

    fn as_any(&self) -> &dyn Any {
        self
    }
}

/// Count how many rules match each provided example and error if any example is unmatched.
pub(crate) fn validate_match_examples(rules: &[RuleRef], matches: &[Vec<String>]) -> Result<()> {
    let mut unmatched_examples = Vec::new();

    for example in matches {
        if rules.iter().any(|rule| rule.matches(example).is_some()) {
            continue;
        }

        unmatched_examples.push(
            try_join(example.iter().map(String::as_str))
                .unwrap_or_else(|_| "unable to render example".to_string()),
        );
    }

    if unmatched_examples.is_empty() {
        Ok(())
    } else {
        Err(Error::ExampleDidNotMatch {
            rules: rules.iter().map(|rule| format!("{rule:?}")).collect(),
            examples: unmatched_examples,
        })
    }
}

/// Ensure that no rule matches any provided negative example.
pub(crate) fn validate_not_match_examples(
    rules: &[RuleRef],
    not_matches: &[Vec<String>],
) -> Result<()> {
    for example in not_matches {
        if let Some(rule) = rules.iter().find(|rule| rule.matches(example).is_some()) {
            return Err(Error::ExampleDidMatch {
                rule: format!("{rule:?}"),
                example: try_join(example.iter().map(String::as_str))
                    .unwrap_or_else(|_| "unable to render example".to_string()),
            });
        }
    }

    Ok(())
}